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Internal head constraint

Relative clauses in English (and in an overwhelming number of languages) obey a `no internal head' constraint. This constraint is exemplified in the contrast between ((226)) and ((227)).
the person [whoi [$\epsilon $C Muriel likes $\epsilon $i]]  (226)0(226
*the person [[which person]i [$\epsilon $C Muriel likes $\epsilon $i]] 

We know of no good way to rule ((227)) out, while still ruling ((228)) in.

the person [[whose mother]i [$\epsilon $C Muriel likes $\epsilon $i]] 

Dayal (1996) suggests that `full' NPs such as which person and whose mother are R-expressions while who and whose are pronouns. R-expressions, unlike pronouns, are subject to Condition C. ((226)) is, then, ruled out as a violation of Condition C since the person and which person are co-indexed and the person c-commands which person. If we accept Dayal's argument, we have a principled reason for allowing overgeneration of relative clauses that violate the internal head constraint, the reason being that the XTAG grammar does generate binding theory violations.

XTAG Project